The following programs are currently under investigation and will be studied further. A. Effects of thyroid hormones in vivo and in vitro on the biosynthesis and metabolism of amino acids and proteins 1. Comparison of the effects of thyroid hormone on concentrations and compositions of amino acids and peptides in blood plasma and various tissues of the rat and guinea pig. 2. Effects of thyroid hormones in vivo and in vitro on the biosynthesis, metabolism, and translocation of some amino acids and peptides. 3. Effects of an amino acid or several amino acids on cellular metabolism and function of the rat and guinea pig in various thyroid hormone states. 4. Effects of thyroid hormones in vivo and in vitro on the formation, function, and catabolism of several enzymes in the rat and guinea pig. B. Study of the mode of action of thyroid hormone in increasing the basal metabolism in conjunction with the roles of NAD-linked and cytochrome-linked L-glycerol-3-P dehydrogenase in cellular metabolism. C. Comparative studies on the effects of thyroid hormone in vivo and in vitro on lipid and cholesterol metabolism in the rat and guinea pig.